A solid polymer electrolyte fuel cell contains a membrane electrode assembly prepared by interposing a solid polymer electrolyte membrane between an anode and a cathode. In this type of fuel cell, the membrane electrode assembly, and a resin frame for supporting the membrane electrode assembly may be integrally bonded to obtain a fuel cell assembly. A plurality of such fuel cell assemblies may be stacked to obtain a stack.
The technique described in Japanese Laid-Open Patent Publication No. 05-234606 has been known as a method for producing such a fuel cell assembly. According to this technique, an opening is formed in a frame-shaped (rectangular) resin frame, a portion in the vicinity of the opening is overlapped on an edge of an electrolyte membrane, and the overlapped portion is heated to form a heat-welded portion.
The electrolyte membrane absorbs and releases water that is generated during an electrode reaction of the fuel cell, whereby the electrolyte membrane is subjected to swelling and shrinkage. In the case that the resin frame and the electrolyte membrane are heat-welded as described in Japanese Laid-Open Patent Publication No. 05-234606, the welded portion of the electrolyte membrane may become denatured by the heat. In this case, the welded portion may become deteriorated in strength and damaged due to such swelling and shrinkage.
In the method proposed in Japanese Laid-Open Patent Publication No. 2008-135295, a portion of a resin frame is melted, the obtained melt is introduced into a gas diffusion layer in an anode or a cathode, and the introduced melt is cooled and solidified. The impact of heat on the electrolyte membrane is reduced in this method, as compared with the aforementioned process of heat-welding the electrolyte membrane directly with the resin frame.
The method described in Japanese Laid-Open Patent Publication No. 2008-135295 will be illustrated schematically. In FIG. 17, reference numeral 10 represents a membrane electrode assembly, and reference numeral 11 represents a resin frame. In this case, the membrane electrode assembly 10 contains a cathode 12, an electrolyte membrane 14, and an anode 16, which are stacked in this order from the bottom.
The cathode 12 contains a gas diffusion layer 18 made of carbon paper or the like, an underlayer 20, and an electrode catalyst layer 22, which are stacked in this order from the bottom. The anode 16 contains an electrode catalyst layer 24, an underlayer 26, and a gas diffusion layer 28 made of carbon paper or the like, which are stacked in this order from the bottom. The cathode 12 is wider than the anode 16, and thus an edge of the upper surface (facing the anode 16) of the electrolyte membrane 14 is exposed outside of the anode 16.
The resin frame 11 has a recess 30 that extends from the lower surface toward the upper surface, and a housing hole 32 formed as a through-hole and which extends from the ceiling surface of the recess 30 to the upper surface. During the process of bonding the resin frame 11 to the membrane electrode assembly 10, the gas diffusion layer 28 of the anode 16 is brought into contact with the ceiling surface of the recess 30, and then the upper surface is heated and pressed in the vicinity of the housing hole 32. A portion of the resin frame 11 is softened (or melted) and is made flowable by heating, such that the softened material penetrates into the gas diffusion layer 28.
Thereafter, the softened material, which is introduced into the gas diffusion layer 28, is solidified, whereby the resin frame 11 is bonded to the gas diffusion layer 28, i.e., to the anode 16.